Affinity absorbents and ultracentrifugation are proposed to provide new approaches to the study of formation and metabolism of fibrinogen-fibrin complexes, and for the detection of occurrence and location of intravascular coagulation in patients and experimental animals. Characterization of the complexes by ultracentrifugation will provide means for subclassifying them according to four types, the distribution of which depends upon the sequence of modification of fibrinogen by thrombin, plasmin, and crosslinking agents. The affinity absorbents will be applied as an aid to isolation of the complexes for characterization of fibrinopeptide and subunit composition both to test identity and to follow changes occurring in blood. The goal of the basic studies will be to assess validity of the proposed role of the complexes in transport and metabolism of fibrin in the circulation and to verify whether the subclassification will extend applicability to detection of abnormalities contributing to pathology. Affinity adsorbents capable of exothermically binding fibrinogen in a reversible and specific manner will be utilized further in developing a simple and rapid means of preparing autologous 131I-fibrinogen for radiologic monitoring of fibrin formation. This application is viewed as providing many advantages over other methods of preparing 131I-fibrinogen currently in use for detection of post surgical thrombosis.